{
 Ivanov Nikita
 18/09/2012
}
program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils;
var
  n,nf, k,kf, i,j:integer;
  c:real;
begin
  nf:=1;
  kf:=1;
  read(n, k);
  for i:=1 to n do
    nf:=nf*i;
  for i:=1 to k do
    kf:=kf*i;
  c:= nf/ (kf*(n-k));
  writeln(c:0:3);
  readln;
end.
